Widodo Widjaja Basuki

Development of sandwich flow channel inserts for an EU DEMO dual coolant blanket concept

Abstract The dual-coolant lead-lithium (DCLL) blanket concept, which is considered as a candidate for fusion power plants and possibly for a demonstration reactor (DEMO), is being investigated within the framework of the European Power Plant Physics and Technology (PPPT) study. One of major issues of the DCLL concept development is the design of the flow channel inserts (FCIs), which are essential for the reduction of magneto-hydrodynamic (MHD) pressure losses. Due to the tight schedule for the short-term PPPT DEMO, a low-temperature DCLL concept with a liquid metal outlet temperature below 500 °C has been proposed. This allows the use of a simpler type of FCI (taking into account the LM corrosion issues), e.g. Eurofer-Alumina-Eurofer sandwich FCI, instead of the SiCf/SiC version for high temperature case, the production thereof is challenging. This paper discusses the technological study on manufacturing of some FCI design variants and post-examination of the samples.

He-Cooled Divertor for DEMO: Technological Study on Joining Tungsten Components with Titanium Interlayer

Abstract A modular He-cooled divertor concept for DEMO has been pursued at KIT with the goal of reaching 10 MW/m2. The reference design uses small tungsten-based cooling fingers of about 20 mm in size. They consist of a tungsten tile as a thermal shield that is to be connected to a thimble heat sink structure from W–1 wt% La2O3 (WL10) tungsten alloy. The lower boundary of the divertor operating temperature window is predicted by the ductile-to-brittle temperature and the upper boundary by the recrystallization temperature of WL10 material, currently assumed at 600°C and 1300°C, respectively. The important requirements for the joint between the W tile and WL10 thimble are (a) functioning as a crack stopper, (b) resisting a high operating temperature of about 1200°C, and (c) using low-activation material as an interlayer. Previously used PdNi brazing material has been successfully tested at a brazing temperature of about 1270°C. The mock-ups produced in this way are sufficient for the HHF tests without neutrons. In a further step to approach the DEMO requirements with higher demands, the use of low-activating titanium with a melting point of 1668°C as bonding material was examined both for brazing and for diffusion welding of tungsten parts. This paper reports on the first successful test results of both high-temperature brazing and diffusion bonding techniques.

Development of Functionally Graded Tungsten/EUROFER Coating System for First Wall Application

Abstract Reduced activation Ferritic/Martensitic (RAFM) steels, e.g. EUROFER are to be used as structural material for the First Wall (FW) of future fusion power plants. The interaction between plasma and FW, especially physical sputtering will limit the FW lifetime under normal operation. Therefore tungsten coating is selected to protect the FW due to its very low sputtering yield and low activation. However, the mismatch in thermo-physical properties between tungsten and EUROFER can lead to large residual thermal stresses and even failure. To overcome the issue of erosion a protective tungsten coating with a functionally graded (FG) tungsten/EUROFER layer (FG tungsten/EUROFER coating system) on EUROFER substrate will be developed and optimized. Non-linear finite element simulations are performed to predict optimal parameters of the coating system. Thereby the potential of the FG-layer in reducing inelastic strains and improving lifetime is demonstrated, and the investigated thickness of FG-layer is suggested. Based on the simulation results samples are fabricated by vacuum plasma spraying (VPS) with three different thicknesses of FG-layer. The microstructural observations revealed that the coating system has fine gradation and variable thickness as designed, low porosity, as well as a sound interface. Berkovich and Vickers hardness identify basic properties of those layers.

Fabrication of Tungsten-Vanadium Hybrid Material with Sufficient Toughness for High-Temperature Applications by Diffusion Bonding

Abstract The design of fusion plasma-facing components is challenging, as their materials have to meet rigorous requirements in terms of low activation and high-temperature strength. At the same time, sufficient ductility is required even in the low-temperature range. Unfortunately, these properties are not found in conventional materials. To solve this problem, a hybrid material that combines the high strength of one material with the high ductility of the other material was developed. This paper presents the hybrid material, which consists of thin tungsten and vanadium layers. This hybrid material was produced by means of diffusion bonding at relatively low temperature in a vacuum chamber. Microstructural investigations and nanoindentation tests indicated no cracks, no delamination, and no brittle intermetallic phases along the bond interfaces. Investigations of the mechanical properties of the hybrid material by instrumented Charpy impact tests revealed a relatively low ductile-to-brittle transition temperature (DBTT) at 124°C (compared to the DBTT of polycrystalline tungsten of >441°C) with an absorbed Charpy impact energy of 4.53 J [kleinst (KLST)-specimen]. Additionally, the tested Charpy impact specimens were found to be not fractured thoroughly even at room temperature.

Recent Progress in the Development of Helium-Cooled Divertor for DEMO

Abstract A helium-cooled divertor concept for DEMO has been continuously developed over the past decade at the Karlsruhe Institute of Technology within the framework of the former European Fusion Power Plant Conceptual Study. Over the years, research results and progress of the divertor development with numerous earnings representations have been continually reported. This paper first gives a retrospect of the past results achieved so far and then reports on recent progress of the divertor development. In the course of developing the conceptual design with the goal of reaching a divertor heat flux performance of 10 MW/m2, the He-cooled modular divertor with jet cooling (HEMJ) was selected in the early 2000s as the reference concept out of a series of conceptual design studies. For verification of the design principle, a combined high-heat-flux (HHF) test facility with helium loop was built in 2004 at the Efremov Institute for the divertor experiments under specified DEMO conditions. There, the cooling performance of the divertor finger with helium under the heat load of 10 MW/m2 was confirmed already at an early stage. In parallel, the HEMJ divertor design was successively improved in terms of its robustness and quality of production in order to achieve a long service life against thermocyclic loading. A breakthrough was achieved in 2010 when an optimized HEMJ cooling finger survived more than 1000 HHF cycles at 10 MW/m2 without damage. In the context of long-term planning for DEMO divertor development, research and development work on the development of larger divertor components has been started, particularly focusing on certain fabrication techniques covering, e.g., high-temperature brazing and mass production of the divertor components. Recent progress—a part of this paper—was achieved in the HHF experiment of the tungsten nine-finger module in Efremov, development of nondestructive testing methods for testing multifinger modules in collaboration with CEA, and a study on the integration of multifinger modules on the target plate.

He-cooled divertor: Study on low-temperature design using Ta alloy as thimble material

A modular He-cooled divertor concept for DEMO has been developed at KIT under the EU PPCS with the goal of reaching 10 MW/m2. The reference design is based on a modular tungsten-based cooling finger, which consists of a tungsten tile as thermal shield brazed to a thimble heat sink made of W-1 wt% La2O3 (WL10). The lower temperature of the divertor operating temperature window is dictated by the ductile-brittle transition temperature and the upper temperature by the recrystallization temperature of WL10 material, assumed at 600 °C and 1300 °C, respectively, under irradiation. In this study, another design option based on the use of tantalum alloy T-111 as an alternative thimble material is investigated, which offers a potential for the exploitation of material ductility, and thus the possibility of a lowering the DBTT temperature limit.

Newly developed innovative manufacturing technologies for He-cooled DEMO divertor

A modular He-cooled divertor concept for DEMO has been developed at Karlsruhe Institute of Technology (KIT). The design goal is to achieve a DEMO-relevant high heat flux of 10 MW/m2. The reference design HEMJ (He-cooled modular divertor with multiple-jet cooling) uses small tungsten-based cooling finger modules. The divertor parts are connected by brazing. They are cooled by helium impinging jets. After the performance and functionality of design has been confirmed through numerous high heat flux (HFF) tests, the current R&D focuses on the manufacturing technology in order to arrive at a robust design and a mass-production of parts. In this paper, newly developed innovative technologies for manufacturing tungsten-based divertor modules (e.g. deep drawing, powder injection molding) as well as for joining the components of different materials shall be presented.